Vinyl ester resin and process for curing same with ionizing radiation in the presence of amines

ABSTRACT

The addition of about 1.5 to 5 weight percent of certain amines to a thermosettable mixture of an alkenyl aromatic monomer and a polymerizable vinyl ester resin reduces the dosage level of ionizing radiation required to cure the mixture.

United States Patent 1 1 [111 3,882,004

Mani 1 May 6, 1975 VINYL ESTER RESIN AND PROCESS FOR CURING SAME WITHIONIZING [56] References Cited RADIATION IN THE PRESENCE OF UNITEDSTATES PATENTS AMINES 2,673,151 3/1954 Gerhart 196/115 P 75 lnder Mani.Midland, Mich 3,301,743 1/1967 Fekete et al. 260/837 R 3,367,992 2/1968Bearden 260/837 R [73] Assignee: The Dow Chemical Company, 3,420,9141/1969 May 260/837 R Midland, Mich. 3,669,911 6/1972 Najvar 260 25 N3,676,398 7/1972 DAlelio 260/837 R 1 1 Flledr 1973 3,683,045 8/1972Baldwin 260/837 R [2ll Appl. Nu: 391,112

Primary ExaminerMurray Tillman Related Application Data AssistantExaminer-Richard B. Turer [62] Division of Ser. No. 143,266, May 13,1971, Pat. No. AtmrneyAgent, 0r Firm- H. L. Aamoth l l ABSTRACT [52] US.Cl 204115916; 117/9331; 117/132 B;

117/l32 BE; 7/161 28; 117/16 U2; The addmon of about 1.5 to 5 weightpercent of cer 204/159; 204/159; 204/5923; tam amines to athermosettable m1xture of an alkenyl I aromatic monomer and apolymerizable vinyl ester [5 I I Int Cl g g fjgz resin reduces thedosage level of ionizing radiation re- [581 Field 61 Search.....204/15915, 159.16, 159.19; qumd cure the 260/836, 837 4 Claims, N0Drawings CROSS-REFERENCE TO RELATED APPLICATION This is a division, ofapplication Ser. No. 143,266, filed May 13, 1971, now U.S. Pat. No.3,810,825.

BACKGROUND OF THE INVENTION This invention relates to the field ofionizing radia tion cure of polymerizable materials and to coatings ofsame and especially relates to a promoter to reduce the ionizingradiation level or dosage necessary to effect a cure of said materials.

From a commercial standpoint radiation curing offers a number ofadvantages over thermal catalystinitiated cures: immediate initiation ofpolymerization, extended pot-life of the curable materials, littletemperature rise so heat sensitive substrates may be employed incoatings, better control of the polymerization reaction, superiorsubstrate-coating bonds are produced and much higher concentrations ofradicals may be produced instantaneously. However, these advantages aredifficult to realize if the curable materials require high curing dosesof ionizing radiation since the economics become prohibitive.Commercialization then depends on reducing the cost of the curingprocess by finding methods and materials to effect a cure at lowerdosages.

The search for means to accelerate or promote radiation curing isevident by a number of patents relating to certain polymerizablematerials. While neither the promoters or the polymerizable materialsemployed correspond in any way to this invention, patents representativeof such efforts include US. Pat. Nos. 3,202,513; 3,251,759; 3,265,604;3,352,771 and 2,979,446. Commercially it is desirable to be able to cureat dosages of no more than 2 to 3 megarads but it would be of greatadvantage to be able to cure at 1 megarad or even less.

SUMMARY OF THE INVENTION According to this invention the curing dosageof ionizing radiation required to cure in an inert atmosphere a mixtureof an alkenyl aromatic monomer and a polymerizable vinyl ester resin isreduced by adding to the mixture at least 0.3 weight percent of certainnitrogen containing materials.

The vinyl ester resin is prepared by reacting about equivalent amountsof a polyepoxide of a polyhydric alcohol having more than one epoxidegroup per molecule with a dicarboxylic acid half ester having theformula 9 9 9 a -g-c-oa o-c-a -coa where R, is hydrogen or an alkylgroup of l to 4 carbons. R is an alkylene group of 2 to 6 carbons and R,is phenylene, cyclohexylene, alkylene or an unsaturated bivalenthydrocarbon radical. The nitrogen materials include various2-oxazolines, guanidines and certain amines which are more fullydescribed hereafter.

DESCRIPTION OF THE INVENTION The general methods by which vinyl esterresins may be prepared are thoroughly described in the patentliterature. Representative patents which describe the resins and theirpreparation include US. Pat. Nos. 3,066,112; 3,179,623; 3,256,226;3,301,743 and 3,377,406.

In particular the vinyl ester resins employed in this invention aredescribed in U.S. Pat. No. 3,367,992 along with methods for theirpreparation. More particularly this invention relates to said resinsprepared from polyepoxides of polyhydric alcohols having more than oneepoxide group per molecule.

The vinyl ester resins are prepared by reaction of about equivalentamounts of said polyepoxide of a polyhydric alcohol and a dicarboxylicacid half ester having the formula 2 e e ca -g-c-oa o-c-s -coa where R,is hydrogen or an alkyl group of l to 4 carbons, R is an alkylene groupof 2 to 6 carbons and R is phenylene, cyclohexylene, alkylene or anunsaturated bivalent hydrocarbon radical.

Said half esters are conveniently prepared by esterification of ahydroxyalkyl acrylate or methacrylate with an equal molar amount of adicarboxylic acid, or preferably a dicarboxylic acid anhydride where itexists. For example, equal molar amounts of 2-hydroxyethyl acrylate andmaleic anhydride may be reacted to form said half ester. Accordingly R,in the formula is usually hydrogen or methyl. In place of 2-hydroxyethylacrylate one may employ hydroxypropyl or hydroxybutyl acrylate ormethacrylate. Also, in place of maleic anhydride or maleic acid one mayemploy fumaric acid, itaconic acid, citraconic acid, adipic acid, theisomeric phthalic acids and the like. The anhydrides of said acids,where available, may also be used.

Said half ester is reacted with a polyepoxide of a polyhydric alcoholhaving more than one epoxide group per molecule. Typical polyhydricalcohols include aliphatic diols (glycols) and the polyalkylene glycolssuch as ethylene glycol, diethylene glycol, triethylene glycol, higherpolyethylene glycols, the analogous propylene glycols and higherpolypropylene glycols, 1,4-butane diol, l,5-pentane diol, neopentylglycol, glycerol, pentaerythritol and the like.

Various catalysts may be used in the preparation of vinyl ester resins.Catalysts include tertiary amines such astris(dimethylaminomethyl)phenol, onium catalysts, triphenyl stibine andtriphenyl phosphine and the like. Usually hydroquinone or other likepolymerization inhibitors are added to prevent polymerization during thepreparation of the resin.

The vinyl ester resin is then mixed with an alkenyl aromatic monomerwhich includes such monomers as styrene, vinyl toluene, halogenatedstyrenes such as ochlorostyrene, vinyl naphthalene, divinyl benzene andthe like.

The polymerizable materials of this invention are especially useful incoating various substrates such as metal, wood and the like either as aprimer coating and- /or a finished coating. In order to obtain thebenefits of this invention at least about 0.3 weight percent of thenitrogen containing material is added to the resin/monomer mixture.Preferably the amount ranges from about 0.3 to 10 weight percent andmost preferably from about 1.5 to 5 weight percent.

When employed as coating formulations other additives may beincorporated into the coating, for example, various inert fillers andpigments such as kaolin clay, titanium dioxide, silica, variousinorganic oxides and the like. Films cast from the coating formulationsmay be rapidly cured by exposing them in an inert atmosphere to ionizingradiation (accelerated particulate radiation). A beam intensity of atleast 50 microamperes is usually employed, but this invention is notlimited thereto and lower beam intensities may be employed.

Generally the films or coatings will range in thickness from about 0.1mil up to about mils. However, depending on the accelerating voltage,thicknesses up to 250 mils or higher are feasible. The radiation curingstep should be performed in an inert atmosphere. By this it is meant anatmosphere which is essentially free of oxygen since the presence ofoxygen may result in an undesirable tacky surface. It is sufficient forthis purpose to place a thin film of a plastic material such as apolyester (Mylar) film on the cast film or coating. Other means may beused such as curing in a chamber containing an essentially oxygen freeatmosphere such as nitrogen, helium, argon and the like.

Accelerated particulate (ionizing) radiation includes particles such aselectrons, protons, deuterons, other ions and the like. However, from anindustrial standpoint, the cost and availability of machines limitionizing radiation curing to accelerated electrons for the immediatefuture. A variety of devices are available to provide acceleratedelectron radiation or varying voltages and beam intensities. Typical ofsuch devices is the familiar Van de Graaff accelerator. Similarcommercial accelerators utilizing various acceleration means areavailable from Texas Nuclear Corporation, (cascade rectified system)High Voltage Engineering, (insulated core transformer system) GeneralElectric (a resonant transformer design) and Radiation Dynamics, Inc.(radio frequency cascade rectifier system).

Nitrogen containing materials include 2-oxazolines, guanidines andcertain amines. Typical of the 2- oxazolines are 2-oxazoline itself, andsubstituted 2- oxazolines having the formula B ll? 16-4! wherein R andR" may be hydrogen, methyl, ethyl, phenyl and the like. R may be analkyl, aryl, aralkyl group or H. Such substituted oxazolines include2-methyl-2-oxazoline; 2,5-diphenyl-2-oxazoline; 2- phenyl,S-methyl-Z-oxazoline; Z-methyl, 5'phenyl-2- oxazoline and the like. Alsoincluded within the term 2-oxazolines are the his oxazolines such as2,2- tetramethylene bis(2-oxazoline); 2,2-oxydiethylenebis(2-oxazoline); 2,2'-thiodiethylene bis(2-oxazoline) and the like.Guanidines include guanidine, tetramethyl guanidine and the like.

Amines which may be employed have the formula R,R R N wherein R, may bean alkyl or an aralkyl group, R and R each may be hydrogen or an alkylgroup or R, and R together may be a cyclic alkylene radical or anoxydialkylene radical. Alkyl groups include methyl, ethyl, propyl,n-butyl, isobutyl and higher alkyl groups. Typical amines include mono-,diand trin-butyl amine, di-isobutyl amine, triethyl amine,cyclohexylamine, benzyl amine, morpholine, piperidine and the like.

The following non-limiting Examples will further illustrate theinvention. All parts and percentages are by weight unless otherwisespecified.

EXAMPLE 1 A vinyl ester resin was prepared by reacting 2- hydroxypropylacrylate (37.5%) with maleic anhydride (34.3%) to form a half esterwhich was subsequently reacted with l,4-butanediol diglycidyl ether(28.2%) according to the procedure of U.S. Pat. No. 3,367,992. The resinwas then mixed with styrene (2 parts/l part). To the mixture was thenadded 3% of a nitrogen containing compound.

A film was cast with a 7 mil drawdown bar on a Q- panel (4 X l2 X .03inches) and covered with a 2 mil sheet of Mylar (polyester) film toexclude air. The coated polished steel Q-panel was then passed through a2 Mev electron beam from a Van de Graaff accelerator filtered with 0.33gm/cm Al. A 50 microampere beam current and a conveyor speed of 3.4cm/sec delivered a dose of 0.1 Megarad (Mrad) for each pass through thebeam.

The curing dose in megarads (Mrad) for each of three different nitrogencompounds is shown below.

Nitrogen Compound Curing Dose, Mrad None 2.8-3.0 Di-n-butyl amine l .4Tetramethyl guanil .3-l .4 dine 2-Oxazoline l 5-] .6

At least about 0.3% of the nitrogen compound is necessary and a minimumcuring dose is found at about 1.5 to 5 weight percent. No advantage isfound with amounts above 10%.

EXAMPLE 2 Another vinyl ester resin was prepared by reacting about equalmolar quantities of Z-hydroxyethyl acrylate and maleic anhydride to forma half ester. The half ester is then reacted with the diglycidyl etherof neopentyl glycol to form a vinyl ester resin.

A series of resin monomer mixtures was prepared with the followingmonomers in 2/1 weight proportions of resin/monomer.

Resin A styrene Resin B vinyl toluene Resin C chlorostyrene (mixture ofortho and para isomers) Resin D divinyl benzene (contained 44% ethylvinyl benzene) Curing Dose, Mrad Nitrogen Compound Resin A Resin B ResinC Resin D 2 l I I l l I It will be understood that the present inventionis not limited to the specific details described above but may embodyvarious modifications insofar as they are defined in the followingclaims.

What is claimed is:

l. A process for curing a mixture of an alkenyl aromatic monomer and apolymerizable vinyl ester resin, said process comprises exposing saidmixture in an inert atmosphere to ionizing radiation said mixture havingadded thereto about to 5 weight percent based on the weight of themixture of an amine having the formula R,R R N where R, is an alkyl oraralkyl group, R, is hydrogen and R may be hydrogen or an alkyl group orR and R together may be a cyclic alkylene radical or an oxydialkyleneradical; and wherein said vinyl ester resin is prepared by reactingabout equivalent amounts of a polyepoxide of a polyhydric alcohol havingmore than one epoxide group per molecule with a dicarboxylic acid halfester having the formula o o o I II I CB C-C-OR 0-0-1: 0011 2 3 1 whereR, is hydrogen or an alkyl group of l to 4 carbons, R is an alkylenegroup of 2 to 6 carbons and R is phenylene, cyclohexylene, alkylene oran unsaturated bivalent hydrocarbon radical.

2. The process of claim 1 wherein R in the amine formula is hydrogen.

3. A thermosettable mixture suitable for curing by exposure to lowlevels of ionization radiation comprising a mixture of an alkenylaromatic monomer and a polymerizable vinyl ester resin, said mixturehaving added thereto about 1.5 to 5 weight percent based on the weightof the mixture of having the formula R,R R;,N where R is an alkyl oraralkyl group, R is hydrogen and R may be hydrogen or an alkyl group orR, and R together may be a cyclic alkylene radical or an oxydialkyleneradical; and wherein said vinyl ester resin is prepared by reactingabout equivalent amounts of a polyepoxide of a polyhydric alcohol havingmore than one epoxide group per molecule with a dicarboxylic acid halfester having the formula 2 e e ca -ze-c-oa o-cm -coa where R is hydrogenor an alkyl group of l to 4 carbons, R is an alkylene group of 2 to 6carbons and R is phenylene, cyclohexylene, alkylene or an unsaturatedbivalent hydrocarbon radical.

4. The mixture of claim I wherein R in the amine formula is hydrogen.

1. A PROCESS FOR CURING A MIXTURE OF AN ALKENYL AROMATIC MONOMER AND APOLYMERIZABLE VINYL ESTER RESIN, SAID PROCESS COMPRISES EXPOSING SAIDMIXTURE IN AN INERT ATMOSPHERE TO IONIZING RADIATION SAID MIXTURE HAVINGADDED THERETO ABOUT 1.5 TO 5 WEIGHT PERCENT BASED ON THE WEIGHT OF THEMIXTURE OF AN AMINE HAVING THE FORMULA R1R2R3N WHERE R1 IS AN ALKYL ORARALKYL GROUP, R2 IS HYDROGEN AND R3 MAY BE HYDROGEN OR AN ALKYL GROUPOR R1 AND R3 TOGETHER MAY BE A CYCLIC ALKYLENE RADICAL OR ANOXYDIALKYLENE RADICAL; AND WHEREIN SAID VINYL ESTER RESIN IS PREPARED BYREACTING ABOUT EQUIVALENT AMOUNTS OF A POLYEPOXIDE OF A POLYHYDRICALCOHOL HAVING MORE THAN ONE EPOXIDE GROUP PER MOLECULE WITH ADICARBOXYLIC ACID HALF ESTER HAVING THE FORMULA
 2. The process of claim1 wherein R3 in the amine formula is hydrogen.
 3. A thermosettablemixture suitable for curing by exposure to low levels of ionizationradiation comprising a mixture of an alkenyl aromatic monomer and apolymerizable vinyl ester resin, said mixture having added thereto about1.5 to 5 weight percent based on the weight of the mixture of having theformula R1R2R3N where R1 is an alkyl or aralkyl group, R2 is hydrogenand R3 may be hydrogen or an alkyl group or R1 and R3 together may be acyclic alkylene radical or an oxydialkylene radical; and wherein saidvinyl ester resin is prepared by reacting about equivalent amounts of apolyepoxide of a polyhydric alcohol having more than one epoxide groupper molecule with a dicarboxylic acid half ester having the formula 4.The mixture of claim 1 wherein R3 in the amine formula is hydrogen.